Physics

The Government of India created the Atomic Energy Establishment, Trombay (AEET) on 3 January 1954. It was established to consolidate all the research and development activity for nuclear reactors and technology under the Atomic Energy Commission. All scientists and engineers engaged in the fields of reactor design and development, instrumentation, metallurgy and material science etc. were transferred with their respective programmes from the Tata Institute of Fundamental Research (TIFR) to AEET, with TIFR retaining its original focus for fundamental research in the sciences. The centre was renamed as the Bhabha Atomic Research Centre (BARC) on 22 January 1967.

India’s First Nuclear Reactor was Apsara. It was also the first nuclear reactor in Asia. Apsara went critical at BARC on August 4, 1956. The reactor was designed by the BARC and built with assistance from the United Kingdom (which also provided the initial fuel supply consisting of 80 percent enriched uranium). It heralded the arrival of India’s nuclear energy programme. Dr. Homi Bhabha himself conceptualised the design of the reactor and the reactor was built entirely by Indian engineers in a record time of about 15 months.

Reactor was named by the then Prime Minister of India, Jawaharlal Nehru when he likened the blue Cerenkov radiation to the beauty of the Apsaras (Indra’s court dancers).

Apsara is a swimming-pool-type reactor loaded with enriched uranium as fuel. The fuel core is suspended from a movable trolley in a pool filled with water. The pool water serves as coolant, moderator and reflector, besides providing the shielding. It was used for various purposes such as production of isotopes; basic research; shielding experiments; neutron activation analysis; neutron radiography and testing of neutron detectors. The Reactor was permanently shutdown in 2010.

The Chernobyl Power Complex, lying about 130 km north of Kiev, Ukraine, consisted of four nuclear reactors of the RBMK-1000 design. On 25 April, prior to a routine shutdown, the reactor crew at Chernobyl 4 began preparing for a test to determine how long turbines would spin and supply power to the main circulating pumps following a loss of main electrical power supply. A series of operator actions, including the disabling of automatic shutdown mechanisms, preceded the attempted test early on 26 April. By the time that the operator moved to shut down the reactor, the reactor was in an extremely unstable condition. The crew initiated an emergency shutdown in response. However the amount of power generated actually rocketed up and blew the seals on the reactor vessel.

Firefighters were on the scene within minutes to contain the blaze, with additional ground teams and helicopters arriving from as far away as Kiev in two hours. By 6:35am, the external fires were extinguished and only the inferno inside Unit 4 continued to burn, as it would for another two weeks. From the second to tenth day after the accident, some 5000 tonnes of boron, dolomite, sand, clay and lead were dropped on to the burning core by helicopter in an effort to extinguish the blaze and limit the release of radioactive particles. Many citizens reported feeling ill by morning, coughing and vomiting involuntarily. It would not be until 2:00pm the following day — nearly 37 hours after the explosion — that officials began moving citizens out of the area. In a matter of hours, the town was empty.

The morning of April 28th, workers nearly 700 miles away at the Forsmark Nuclear Power Plant in Sweden were stopped when trace amounts of radioactive material were found on their clothes. Swedish administrators discovered by midday that the isotopes were from another location. In time, the fallout would reach as far away as the mountainous regions of Scotland, exposing Europeans to harmful radiation largely without their knowledge — and, until the Swedes brought their information onto the national stage, without a Soviet admission of guilt.

Two objects exert a force of attraction on one another known as “gravity.” Sir Isaac Newton quantified the gravity between two objects when he formulated his three laws of motion. Yet Newton’s laws assume that gravity is an innate force of an object that can act over a distance. In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. As a result, he found that space and time were interwoven into a single continuum known as space-time. Events that occur at the same time for one observer could occur at different times for another.

Einstein then spent ten years trying to include acceleration in the theory and published his theory of general relativity in 1915. In it, he determined that massive objects cause a distortion in space-time, which is felt as gravity. Einstein proposed that objects such as the sun and the Earth change the geometry. In the presence of matter and energy it can evolve, stretch and warp, forming ridges, mountains and valleys that cause bodies moving through it to zigzag and curve. So although Earth appears to be pulled towards the sun by gravity, there is no such force. It is simply the geometry of space-time around the sun telling Earth how to move.

Although instruments can neither see nor measure space-time, several of the phenomena predicted by its warping have been confirmed. Light around a massive object, such as a black hole, is bent, causing it to act as a lens for the things that lay behind it. Astronomers routinely use this method to study stars and galaxies behind massive objects. Einstein’s Cross, a quasar in the Pegasus constellation, is an excellent example of gravitational lensing. The quasar is about 8 billion light-years from Earth, and sits behind a galaxy that is 400 million light-years away. Four images of the quasar appear around the galaxy because the intense gravity of the galaxy bends the light coming from the quasar. The general theory of relativity also explains the motion of the planets and can also describe the history and expansion of the universe.